Bull semen in vitro fertility after cryopreservation using egg yolk LDL: a comparison with Optidyl 1 , a commercial egg yolk extender Lamia Amirat a , Daniel Tainturier a , Lae ¨titia Jeanneau a , Chantal Thorin a , Olivier Ge ´rard b , Jean Luc Courtens c , Marc Anton d,* a Laboratory of Biotechnology and Pathology of Reproduction, National Veterinary School of Nantes, BP 40706, 44307 Nantes, France b Ouest Ge ´ne ´tique Elevage Reproduction (OGER), La Bossie ´rie, B.P 80, 44130 Blain, France c Institut National de la Recherche Agronomique (INRA), Physiologie de la Reproduction et des Comportements, Nouzilly 37 380, France d Groupe Physico-chimie des Emulsions, Laboratoire d’Etude des Interactions des Mole ´cules Alimentaires, Institut National de la Recherche Agronomique (INRA), BP 71627, 44316 Nantes Cedex 3, France Received 7 May 2003; received in revised form 1 July 2003; accepted 9 July 2003 Abstract Low-density lipoproteins (LDL) have been previously isolated and identified as the cryoprotective fraction of yolk. The effect of LDL on sperm motility after freezing–thawing has been reported, but no study has been made to assess the effect of LDL on bull semen fertility. The aim of this study was to evaluate the fertility of bull semen cryopreserved in the presence of LDL. Motility of semen cryopreserved in LDL was analyzed and compared to semen cryopreserved with Optidyl 1 ,a commercial extender containing egg yolk. To evaluate the fertilizing ability of semen, we used in vitro fertilization test, whereas acrosome and plasma membrane integrity were also evaluated. The percentage of motile spermatozoa was two fold higher after freezing in LDL than in Optidyl 1 54.4% versus 30.2% (P < 0:05). The cleavage rate was significantly higher after fertilization with semen frozen in LDL than with Optidyl 1 63.0% versus 54.8% (P < 0:05). No significant difference was observed on the blastocyst rate after in vitro culture. Integrity of the acrosome and the plasma membrane were maintained in both extenders. In conclusion, LDL preserve bull semen quality and fertilizing ability, allowing also better semen motility, after the freeze–thaw process. # 2003 Elsevier Inc. All rights reserved. Keywords: Bull semen; Cryopreservation; Yolk LDL; Sperm motility; Fertility; Acrosome integrity Theriogenology 61 (2004) 895–907 * Corresponding author. Tel.: þ33-2-40-67-50-80; fax: þ33-2-40-67-50-84. E-mail address: anton@nantes.inra.fr (M. Anton). 0093-691X/$ – see front matter # 2003 Elsevier Inc. All rights reserved. doi:10.1016/S0093-691X(03)00259-0